1. Field of the Invention
The invention relates to a measuring device, and specifically, to a device for measuring linear displacement of a screw mechanism.
2. Description of the Related Art
Screw mechanisms have the capability of converting rotational motion into linear motion. Specific examples of screw mechanisms include leadscrews, ball screws, jackscrews, rack and pinions, etc.
Compared to other mechanisms capable of realizing linear motion, the screw mechanism provides a large speed reduction ratio, and a small linear displacement value associated with a large rotation angle. Driven by the development of modern manufacturing industry, highly precise driving and positioning can be readily realized with screw mechanisms, and thus screw mechanisms are widely used in the fields of precision instruments.
In order to quantify linear displacement in general, direct length measuring devices are widely utilized. These include linear grating, magnetic grating, induction synchronizer, and so on. In addition, indirect length measuring devices are also known, by which the rotation angle is measured first, and then the linear displacement value is obtained through scale conversion. However, conventional indirect length measuring devices must be installed perfectly parallel and concentric to the motion direction of the screw mechanism to avoid generating large measuring errors.
For applications utilizing horizontal screw mechanisms, a hand wheel gravity-based vertical position indicator has been developed by Siko. Based on the principle of gravity, a free oscillating pendulum set inside the indicator drives a gear system to transfer motion of the oscillating pendulum to a pointer. However, the application of a gear, a pointer, and a dial indicating system limits the measuring resolution and accuracy. Therefore, much opportunity for improvement exists in the field of measuring linear motion of horizontal screw mechanisms.